I claim the ornamental design for a toilet tank, as shown and described.
FIG. 1 is a perspective view of another embodiment of the claimed design;
FIG. 2 is a front view of the embodiment of FIG. 1;
FIG. 3 is a rear view of the embodiment of FIG. 1;
FIG. 4 is a side view of the embodiment of FIG. 1;
FIG. 5 is another side view of the embodiment of FIG. 1;
FIG. 6 is a top view of the embodiment of FIG. 1; and,
FIG. 7 is a bottom view of the embodiment of FIG. 1.
The ornamental design which is claimed is shown in solid lines in the drawings. The broken lines in the drawings are for illustrative purposes only and form no part of the claimed design. Broken lines formed of unequal length dashes (i.e., dash-dot) define bounds of the claimed design.